Process Quality Control Strategy for the Phase-2 Upgrade of the CMS Outer Tracker and High Granularity Calorimeter

Between 2025 and 2027, some essential components of the CMS (Compact Muon Solenoid) detector - most notably the tracker and the calorimeter endcap - will be upgraded to prepare for HL-LHC (High Luminosity Large Hadron Collider) conditions. The upgraded CMS Outer Tracker and parts of the new CMS High Granularity Calorimeter (HGCAL) will encompass over $50{,}000$ new silicon sensors covering a total area of about $800\,\text{m}^{2}$. The sensor series production requires a dedicated strategy to monitor the quality and stability of the production process. The strategy is based on a test structure set that provides quick and easy access to critical process parameters. These include parameters not directly accessible on the sensors (e.g. oxide charge concentration and interface trap density) and parameters requiring potentially destructive measurements (e.g. dielectric strength). The set is implemented at least twice on each production wafer. It is divided into test structures for initial evaluation of the most relevant process parameters and structures for in-depth analysis. All structures can be contacted using a 20-needle probe card and an automated positioning stage. With this system, the initial analysis of one wafer is possible in about 30 minutes. In this paper, the CMS collaboration presents the quality assurance plan for the Phase-2 Upgrade with a focus on process quality control. We cover sensor process specifics, the layout of the test structure set that will be implemented in the production runs for the CMS Outer Tracker and HGCAL, and measurement results illustrating the functionality of the included test structures.Comment: 6 pages, 7 figures, 2 tables, submitted to Nuclear Inst. and Methods in Physics Research A, Proceedings of the 12th International Hiroshima Symposium on Development and Application of Semiconductor Tracking Detector

Development of LGAD sensors with a thin entrance window for soft X-ray detection

We show the developments carried out to improve the silicon sensor technology for the detection of soft X-rays with hybrid X-ray detectors. An optimization of the entrance window technology is required to improve the quantum efficiency. The LGAD technology can be used to amplify the signal generated by the X-rays and to increase the signal-to-noise ratio, making single photon resolution in the soft X-ray energy range possible. In this paper, we report first results obtained from an LGAD sensor production with an optimized thin entrance window. Single photon detection of soft X-rays down to 452~eV has been demonstrated from measurements, with a signal-to-noise ratio better than 20.Comment: 10 pages, 6 figure

Characterization of iLGADs using soft X-rays

Experiments at synchrotron radiation sources and X-ray Free-Electron Lasers in the soft X-ray energy range ($250$eV--$2$keV) stand to benefit from the adaptation of the hybrid silicon detector technology for low energy photons. Inverse Low Gain Avalanche Diode (iLGAD) sensors provide an internal gain, enhancing the signal-to-noise ratio and allowing single photon detection below $1$keV using hybrid detectors. In addition, an optimization of the entrance window of these sensors enhances their quantum efficiency (QE). In this work, the QE and the gain of a batch of different iLGAD diodes with optimized entrance windows were characterized using soft X-rays at the Surface/Interface:Microscopy beamline of the Swiss Light Source synchrotron. Above $250$eV, the QE is larger than $55\%$ for all sensor variations, while the charge collection efficiency is close to $100\%$. The average gain depends on the gain layer design of the iLGADs and increases with photon energy. A fitting procedure is introduced to extract the multiplication factor as a function of the absorption depth of X-ray photons inside the sensors. In particular, the multiplication factors for electron- and hole-triggered avalanches are estimated, corresponding to photon absorption beyond or before the gain layer, respectively.Comment: 16 pages, 8 figure

First operation of the JUNGFRAU detector in 16-memory cell mode at European XFEL

The JUNGFRAU detector is a well-established hybrid pixel detector developed at the Paul Scherrer Institut (PSI) designed for free-electron laser (FEL) applications. JUNGFRAU features a charge-integrating dynamic gain switching architecture, with three different gain stages and 75 μm pixel pitch. It is widely used at the European X-ray Free-Electron Laser (EuXFEL), a facility which produces high brilliance X-ray pulses at MHz repetition rate in the form of bursts repeating at 10 Hz. In nominal configuration, the detector utilizes only a single memory cell and supports data acquisition up to 2 kHz. This constrains the operation of the detector to a 10 Hz frame rate when combined with the pulsed train structure of the EuXFEL. When configured in so-called burst mode, the JUNGFRAU detector can acquire a series of images into sixteen memory cells at a maximum rate of around 150 kHz. This acquisition scheme is better suited for the time structure of the X-rays as well as the pump laser pulses at the EuXFEL. To ensure confidence in the use of the burst mode at EuXFEL, a wide range of measurements have been performed to characterize the detector, especially to validate the detector alibration procedures. In particular, by analyzing the detector response to varying photon intensity (so called ‘intensity scan’), special attention was given to the characterization of the transitions between gain stages. The detector was operated in both dynamic gain switching and fixed gain modes. Results of these measurements indicate difficulties in the characterization of the detector dynamic gain switching response while operated in burst mode, while no major issues have been found with fixed gain operation. Based on this outcome, fixed gain operation mode with all the memory cells was used during two experiments at EuXFEL, namely in serial femtosecond protein crystallography and Kossel lines measurements. The positive outcome of these two experiments validates the good results previously obtained, and opens the possibility for a wider usage of the detector in burst operation mode, although compromises are needed on the dynamic range

Prozessqualitätskontrolle für Siliziumsensoren für das CMS Phase-2-Upgrade

Abweichender Titel nach Übersetzung der Verfasserin/des VerfassersDer Start des High Luminosity Large Hadron Colliders (HL-LHC) der Europäischen Organisation für Kernforschung (CERN) im Jahr 2027 wird eine neue Era für die Hochenergie- Teilchenphysik einläuten. Zur Vorbereitung auf die Herausforderungen, die mit der wesentlich erhöhten Luminosität einhergehen, werden die Physikexperimente am LHC zwischen 2025 und 2027 einem großangelegten Upgrade unterzogen.Für das CMS (Compact Muon Solenoid) Experiment bedeutet das Upgrade unter anderem den vollständigen Tausch des Siliziumspurdetektors und der Kalorimeter-Endkappen. Zwischen 2020 und 2023 gehen deshalb mehr als 50 000 großflächige, positionssensitive Siliziumsensoren in Produktion und werden anschließend in den äußeren Spurdetektor und das neue High Granularity Calorimeter (HGCAL) eingebaut.Die Sensoren unterliegen während des gesamten Produktionszeitraums einer genauen Qualitäts- und Stabilitätskontrolle. Die vorliegende Dissertation befasst sich mit der von CMS verfolgten Strategie der Prozessqualitätskontrolle. Die Überwachung kritischer Prozessparameter erfolgt mithilfe von Teststrukturen, die auf denselben Wafern gefertigt werden, wie die zu testenden Sensoren. Dadurch wird gewährleistet, dass Teststrukturen und Sensoren dieselben Eigenschaften aufweisen. Die Teststrukturen erlauben einen einfachen Zugang zu Prozessparametern, darunter auch solche Parameter, die auf den Sensoren nicht direkt bestimmbar sind (z.B. die Konzentration fixer Ladungsträger im Oxid oder die Rekombinationsgeschwindigkeit von Ladungsträgern an der Halbleiteroberfläche) sowie Parameter, die destruktive Messmethoden erfordern (z.B. die Durchbruchspannung des Oxids).Den Kern dieser Arbeit bildet das Design eines Sets von Teststrukturen zur automatisierten Kontrolle aller relevanten Prozessparameter für die Serienproduktion von CMS Siliziumsensoren. Das Set ermöglicht die Erhebung der wichtigsten Prozessparameter in rund 30 Minuten pro Wafer und erlaubt eine tiefergehende Analyse im Fall von Problemen. Das Set ist auf automatisierte Messungen mit einer Nadelkarte zugeschnitten.Für die Entwicklung des Sets wurden unterschiedlichste Teststrukturen, produziert von zwei verschiedenen Halbleiterherstellern, elektrisch vermessen und Simulationen durch- geführt. Dabei wurde ein besonderer Fokus darauf gelegt, im finalisierten Set mehrere verschiedene Teststrukturen anzubieten, um einzelne Prozessparameter zu extrahieren und so einander gegenseitig ergänzende Messansätze bereitzustellen.Die ersten realen Instanzen des Sets auf Produktionswafern für den äußeren CMS Spurdetektor und Wafern mit HGCAL Prototypsensoren wurden einer systematischen Analyse unterzogen. Damit konnte die Funktionalität des Sets und aller enthaltenen Teststrukturen gezeigt werden. Diese Ergebnisse erlauben es, die Unterschiede der Produktionsprozesse für den äußeren CMS Spurdetektor und HGCAL zu quantifizieren. Zusätzlich geben die Messungen Aufschluss über Defizite des aktuellen Designs des Sets und bereiten die Grundlage für entsprechende Verbesserungsmaßnahmen.Das Teststrukturset und die hier präsentierten Ergebnisse emöglichen die Standardisierung der CMS Prozessqualitätskontrolle. Die Vergleichbarkeit der Messungen zwischen den verschieden CMS Testzentren kann so über die gesamte Laufzeit der Produktion gesichert werden. Zusammen mit direkten Sensormessungen und Tests nach Bestrahlung, sichert die hier dargelegte Methode zur Prozessqualitätskontrolle die Qualität der Siliziumsensoren, die in den CMS Spurdetektor und HGCAL eingebaut werden und leistet letztendlich einen nicht unwesentlichen Beitrag für die künftige Suche nach neuer Physik am HL-LHC.The start of the High Luminosity Large Hadron Collider (HL-LHC) at the European Organization for Nuclear Research (CERN) scheduled for 2027 will herald a new era for high energy particle physics. The physics experiments located at the LHC will undergo a major upgrade between 2025 and 2027 to ready for the challenging conditions of the new high luminosity environment.As part of this upgrade, the CMS (Compact Muon Solenoid) experiment will see the complete replacement of the full silicon tracker and the calorimeter endcaps. Over 50 000 large-area, position-sensitive silicon sensors will be produced between 2020 and 2023 to be integrated into the CMS Outer Tracker and the new High Granularity Calorimeter (HGCAL).This thesis presents the CMS strategy to monitor the quality and stability of the sensor manufacturing process throughout production time. The process quality control procedure relies on tracking critical process parameters on test structures. The structures are manufactured on the same wafers as the sensors and, hence, share the same properties. They provide easy access to many process parameters, including parameters that are not directly accessible on sensors (e.g. oxide charge concentration and surface generation velocity) and parameters that require destructive measurements (e.g. dielectric breakdown voltage).The main part of this thesis establishes a set of test structures designed to allow automated assessment of a comprehensive set of process parameters. This test structure set constitutes the basis of CMS silicon sensor process quality control. It facilitates quick assessment of critical process parameters in about 30 minutes per wafer and provides the means for in-depth analysis in case of any irregularities detected. Measurements of the set utilize a 20-needle probe card and an automated positioning stage.The development process of the test structure set combined electrical measurements on individual test structures manufactured on prototype wafers by two different foundries and simulations of test structure response to the variation of different process parameters. Specific emphasis was put on investigating the capability of different test structures to access the same process parameters, aiming at providing complementary measurement methods within the finalized set.Measurements of the first instances of the set produced on CMS Outer Tracker production wafers and HGCAL prototype wafers have demonstrated the functionality of the set and the included test structures. The results serve to quantify process related differences of the wafer material for the CMS Outer Tracker and HGCAL. Based on these measurements, the shortcomings of the current design of the test structure set are identified and mitigation measures are proposed.The test structure set and the results presented in this thesis have served to standardize the process quality control procedure and to ensure cross-comparability between different test centers within the CMS silicon sensor working groups and over the full series production time. Together with direct electrical measurements of the manufactured sensors and irradiation tests, the presented process quality control procedure will ensure the quality of the silicon sensors integrated into the CMS Outer Tracker and HGCAL and, ultimately, will aid the search for new physics at the HL-LHC.15

Charge sharing studies of silicon strip sensors for the CMS phase II upgrade

Zusammenfassung in deutscher SpracheDas CMS Experiment am CERN steht als eines von vier großen Experimenten am Large Hadron Collider (LHC) vor zahlreichen Herausforderungen. Wissenschaftliche Zielsetzungen, wie Higgs-Präzisionsmessungen und die Suche nach neuer Physik jenseits des Standardmodells, machen es erforderlich, den LHC mit höherer Luminosität zu betreiben als zuvor. Die daraus erwachsenden Anforderungen müssen von CMS erfüllt werden. Das betrifft einerseits die Strahlenschäden am CMS Detektor und andererseits die erhöhte Anzahl an Kollisionen pro Frequenzintervall, welche die Rekonstruktion der Spuren von entstehenden Zerfallsprodukten erschweren. Mit geplantem Beginn ab 2023 werden im Rahmen des CMS Phase II Upgrades die notwendigen Anpassungen des CMS Detektors durchgeführt. Zu diesem Zeitpunkt wird auch der CMS Silizium-Tracking-Detektor das Ende seiner vorgesehenen Lebenszeit erreicht haben und vollständig erneuert werden. Die dort neu eingesetzten Siliziumsensoren müssen im extrem strahlungsbelasteten Milieu des High Luminosity LHC störungsfrei funktionieren. Zu diesem Zweck werden künftig, anstelle der aktuell verwendeten n-Typ Sensoren, p-Typ Siliziumstreifensensoren, welche sich insgesamt als stabiler gegenüber Strahlenschäden erwiesen haben, am CMS Tracker eingesetzt werden. Dementsprechend ist das Bestreben groß, p-Typ Siliziumstreifensensoren mit n+-Streifen einsatzbereit für den Betrieb im neuen CMS Tracker zu machen. Diese Sensoren vom Typ n-in-p benötigen eine spezielle Struktur mit hoher p+-Dotierkonzentration, das sogenannte p-stop, zur elektrischen Separation der einzelnen Streifen. Für bestmögliches Sensorverhalten muss das p-stop Layout optimiert werden. Als Hauptziel dieser Arbeit wurden mehrere Prototyp-Sensoren mit verschiedenen p-stop Geometrien und unterschiedlichen Implantationstiefen und Konzentrationen mithilfe eines Lasersystems sowie mit geladenen Teilchen aus einer radioaktiven 90Sr-Quelle getestet. Um diese Tests zu ermöglichen, wurde ein kürzlich erworbenes Sensor-Auslesesystem am Institut für Hochenergiephysik in Wien in Betrieb genommen. Die zugehörige Datenanalysesoftware wurde angepasst und weiterentwickelt, um die Anforderungen, die aus positionsauflösenden Laserscans erwachsen, zu erfüllen. Mit diesem System wurden anschließend Vergleichsstudien mit den Prototyp-Sensoren durchgeführt und Eigenschaften wie die Aufteilung von Ladung zwischen benachbarten Streifen sowie Ladungsverluste an der p-stop Schicht untersucht. Anhand dieser Untersuchungen wird als Abschluss der vorliegenden Diplomarbeit eine mögliche Layoutkonfiguration vorgeschlagen, um die Performance der p-stop Schicht in Bezug auf die untersuchten Parameter zu optimieren. Diese Ergebnisse werden künftig von Bedeutung für weiterführende Entwicklungsschritte auf dem Weg zum neuen CMS Tracker sein.As one of the four large experiments at the LHC at CERN the CMS experiment is met with many challenges. Physics goals like precision Higgs studies and the search for physics beyond the Standard Model demand for the LHC to run at higher luminosities than before. CMS is now faced with the challenge to fulfil the requirements that come with the High Luminosity LHC. These include the radiation damage to the CMS detector and the increased number of collisions per bunch crossing, which make it more difficult to reconstruct the tracks of resulting decay products. The necessary adaptations to CMS will take place during the CMS Phase II Upgrade scheduled to start in 2023. By this time the CMS silicon tracker will have reached the end of its designated life time and will be replaced entirely. The newly installed silicon sensors have to ensure a smooth operation in the harsh radiation exposed environment of the High Luminosity LHC. For this purpose the CMS tracker will employ p-type silicon sensors, as they are known for a more resilient behaviour under irradiation than the currently installed n-type variant. Thus, high efforts are put into making p-type silicon strip sensors with n+-strip implants fit for the incorporation in the new CMS silicon tracker. These n-in-p type sensors require a special structure of high p+ doping concentration, the so-called p-stop, to electrically separate the individual strips. To achieve the best possible performance of the sensors, this p-stop layout has to be optimised. As the main goal of this thesis I tested a number of prototype sensors with various geometric p-stop layouts and varying implant depths and concentrations, employing an infrared laser system and a 90Sr radioactive charged particle source. To facilitate these tests, I commissioned a newly purchased sensor readout system at the Institute of High Energy Physics in Vienna and adapted and enhanced the data analysis software to fit the needs of position sensitive laser scanning. With this system I subsequently conducted comparative studies with the prototype sensors, investigating properties like charge sharing between neighbouring strips and the phenomenon of charge loss at the p-stop layer. From these investigations, as a conclusion of this thesis, I move on to propose a possible layout configuration to optimise the performance of the p-stop layer with respect to these parameters. The such obtained results will be important for subsequent development steps along the way toward the upgraded CMS tracker.8

Measurements of surface and bulk radiation damage effects in silicon detectors for Phase-2 CMS Outer Tracker

In this work we address the effects of bulk and surface damages on detectors fabricated by Hamamatsu on standard float zone (FZ) p-type material with an active thickness of 290 $\mu$m or thinned to 240 $\mu$m. In order to disentangle the effects of the two main radiation damage mechanisms, ionization effects and atomic displacement, the structures underwent two types of radiation: X-ray with doses from 0.05 to 70 Mrad (SiO$_2$) and neutron in the range of 1$-$10 $\times$ 10$^{14}$ n$_{eq}$/cm$^2$ 1 MeV equivalent. The combined surface and bulk damage could be investigated in structures that underwent both types of irradiation. A wide set of measurements has been carried out on the test structures for a complete characterization.In this work we address the effects of bulk and surface damages on detectors fabricated by Hamamatsu on standard float zone (FZ) p-type material with an active thickness of 290 µm or thinned to 240 µm. In order to disentangle the effects of the two main radiation damage mechanisms, ionization effects and atomic displacement, the structures underwent two types of radiation: X-ray with doses from 0.05 to 70 Mrad (SiO 2 ) and neutron in the range of 1 − 10 × 10 14 n eq /cm 21MeV equivalent. The combined surface and bulk damage could be investigated in structures that underwent both types of irradiation. A wide set of measurements has been carried out on the test structures for a complete characterization

Results of the 2022 ECFA Early-Career Researchers Panel survey on career prospects and diversity

International audienceThis document presents the outcomes of a comprehensive survey conducted among early career researchers (ECRs) in academic particle physics. Running from September 24, 2022, to March 3, 2023, the survey gathered responses from 759 ECRs employed in 39 countries. The study aimed to gain insights into the career prospects and experiences of ECRs while also delving into diversity and sociological aspects within particle physics research. The survey results are presented in a manner consistent with the survey choices. The document offers insights for the particle physics community, and provides a set of recommendations for enhancing career prospects, fostering diversity, and addressing sociological dimensions within this field